Posted on by David Dickinson

A Hybrid Solar Eclipse Seen From Earth… and Space

The Elektro-L satellite's view of how the Nov. 3, 2013 solar eclipse effected Earth. Blackness from the eclipse covers Africa. Credit: Elektro-L/Vitaliy EgorovVitaliy Egorov.

The final eclipse for 2013 was a grand event, witnessed across the Atlantic and the heart of Africa this past Sunday. Like so many other photographers along the North American east coast, we were at the ready to greet the partially eclipsed Sun at dawn. And as the shadow of the Moon touched down, teams on land, air and sea were ready to meet with the fleeting umbra as it raced eastward towards sunset over the Horn of Africa region.

But a fleet of spacecraft were also on hand to witness the rare spectacle as well. Turned earthward and sunward, these spacecraft documented not only the passage of the Moon’s shadow over the Earth, but recorded multiple partial solar eclipses from orbit as well.

The first view comes from the Roscosmos Electro-L satellite based in a geostationary orbit over the Indian Ocean:

Electro-L had captured such a view before, during the annular eclipse over Australia earlier this year in May. Roscosmos increased the frame capture rate of Electro-L to twice its usual speed for the sequence. As you watch the Earth pass from a waning gibbous to crescent phase, you can just see the umbra, or central shadow of the Moon, slide into view and come into contact with the sunset terminator over eastern Africa. You can also see the cloud cover that marks the dust storms that plagued eclipse-chasers based around the Lake Turkana region in Kenya.

One of the first public pictures of the umbra of the Moon as seen from space was taken from the Mir space station during a total solar eclipse in 1999. To our knowledge, such a feat has yet to be duplicated aboard the International Space Station. The phase angle of the ISS’s orbit during the eclipse was nearly perpendicular to the Sun-Moon-Earth syzygy, and unfavorable for this particular eclipse.

Thanks to the Russian journalist Vitaliy Egorov for bringing the Electro-L eclipse sequence to the attention of Universe Today!

Next up is a sequence of images from NASA’s Aqua satellite:

Sunday's eclipse and the Moon's umbra as seen from the Aqua satellite. (Credit: NASA/GSFC/Jeff Schmaltz/MODIS Land Rapid Response Team).
Sunday’s eclipse and the Moon’s umbra off of the west coast of Africa as seen from the Aqua satellite. (Credit: NASA/GSFC/Jeff Schmaltz/MODIS Land Rapid Response Team).

Launched in 2002, Aqua is part of the “A-train” (as in “Afternoon”) constellation of Earth-observing satellites. Perched in a low-Earth Sun-synchronous orbit, Aqua caught sight of the umbra of the Moon at around 14:45 UT on Sunday, November 3rd as it raced to make first landfall over the nation of Gabon and awaiting eclipse chasers.

Some Sun observing spacecraft caught sight of the eclipse as well. The European Space Agency’s Proba-2 nabbed three partial solar eclipses from its vantage point in low Earth orbit:

PROBA-2 used its SWAP imager to grab the sequences. Orbiting the Earth once every 99 minutes or 14.5 time a day, these “orbital eclipses” are quick, lasting about 10 minutes each in duration.

Finally, EUMETSAT’s MeteoSat-10 meteorological satellite based in a geostationary orbit over Africa captured an outstanding sequence, showing nearly the entire trek of the umbra across the entire path of the eclipse:

The sequence runs from 7:30 to 18:30 UT on November 3rd. Note how the video shows the shadow fade in and sharpen as the eclipse touches down off of the US East Coast and intensifies from an annular to total along the first 15 seconds of its track, only to speed up and flatten towards sunset over Africa. And all in six seconds!

And back here on Earth, we couldn’t resist stitching together the bounty from our own minor eclipse expedition for a stop-motion view of the partially eclipsed Sun rising over the Vehicle Assembly Building at the Kennedy Space Center in Florida:

We’d like to also mention a photo that isn’t a “solar eclipse seen from space…” Y’know the one, which shows the Earth, the Moon’s shadow, and a totally-eclipsed Sun, against a star dappled Milky Way. We won’t dignify it with a link. This has already been debunked by Bad Astronomer himself Phil Plait, but the bogus pic now seems to make its rounds across ye’ ole Web now during every eclipse. Seriously? Do we all crave “link juice” that bad? There are lots of real awesome eclipse photos out there, from Earth & beyond! Please, do your part to tell that well meaning friend/coworker/relative/stranger on Twitter that this “ultimate eclipse photo…” isn’t.

How rare are hybrid solar eclipses? Well, the next solar eclipse that is both annular and total along its track occurs over southeast Asia on April 20th, 2023. It’s interesting to note that this past weekend’s eclipse may have been the first sunrise solar eclipse over the VAB since it was built in 1966. Eclipses in the same 18 years and 11 days- long saros cycle repeat, but move about 120 degrees westward. Thus, follow an eclipse cycle through a “triple saros”— known as an “Exeligmos,” an ultimate scrabble word if you can land it on a triple word score! —and an eclipse’s geometry will roughly line back up over a 54 year 33 day long span. Saros 143 produced a an eclipse crossing a similar path on October 2nd, 1959 (before the VAB was built!) and will repeat its Atlantic sunrise performance on December 6th, 2067! Let’s see, by then I’ll be…

Posted on by David Dickinson

Watch Live: Sunday’s “Hybrid Solar Eclipse”

Totality! As seen during the November 13th, 2012 total solar eclipse. (Image credit: Narayan Mukkavilli, used with permission).

The chase is on. On Sunday, November 3rd, the shadow of the Moon will cross the Earth for one last time in 2013. We recently wrote about the prospects for viewing this “hybrid” annular-total solar eclipse as it crosses the Atlantic and central Africa. Viewers from northern South America across the U.S. Eastern Seaboard up into the Canadian Maritimes will also be treated to a brilliant rising partial eclipse over the Atlantic at sunrise. Tickets are already in hand for many, as umbraphiles wing their way (cue Indiana Jones music) to dusty and exotic far off locales to stand briefly in the shadow of our Moon…

But what if it’s cloudy?

Once the bane of eclipse-chasers, you can now thwart our sometimes murky atmosphere by catching the solar eclipse online.

I remember our first experience with eclipse-chasing on the internet, trying to catch an eclipse broadcast on ye ole dial up modem from an internet café (remember internet cafes?) way back in the late 90s. This was pre-You Tube, pre-UStream. Needless to say, the tenuous connection afforded nary a frozen glimpse of the partially eclipsed Sun, and crashed all together at the onset of totality.

Fast forward to 2013, when ginormous data packets routinely fly around the globe.

True, this eclipse presents a challenge, as it crosses some pretty wild and unconnected terrain. But one standby that we can expect is the good people at Slooh, who have dispatched a broadcast team to the African nations of Gabon and Kenya:

As of this writing, Slooh looks to be going live at around 11:45 UT on Sunday November 3rd. This is 6:45 AM EST, which takes into account our “falling back” one hour to UT -5 hours on Sunday morning. Astronomer Brian Cox will be broadcasting live from Kenya, and the broadcast starts just over two hours prior to the first landfall of totality at just before 14:00 UT. From Gabon, Maximum totality will be a brief 1 minute and 5 seconds, and will dwindle to an even briefer 14 seconds over Lake Turkana in Kenya before ending as a brilliant sunset eclipse over Somalia and Ethiopia. A backup broadcast of the partial phases of the eclipse is also planned from Slooh’s home base site in the Canary Islands.

Another fascinating potential broadcast may come our way from the BRCK organization basing their observations of the eclipse from the shores of Lake Turkana in Kenya.  Billed as “Your Backup Generator for the Internet,” BRCK’s mission is to bring broadband access internet to people in remote regions of the world. This weekend’s eclipse certainly qualifies. As of writing this on Halloween, October 31st, the BRCK team had gone into the field to “stress test” their webcasting capability onsite; follow them on Twitter as @brcknet for the latest updates. As of yet, there’s no embed for the broadcast, though we’ll be sure to drop it in if it surfaces!

There’s also some interesting science afoot during this eclipse as well. A recent press release out from Williams College notes that Field Memorial Professor of Astronomy and chair of the International Astronomical Union’s Working Group on Eclipses Jay Pasachoff will observe the eclipse, along with a student and tourist expedition from Gabon. A veteran eclipse chaser, Pasachoff will be working in concert with Dr. Vojtech Rusin of the Astronomical Institute of Slovakia, solar researchers Aris Voulgaris and Robert Lucas and William College students to study the ethereal solar corona.  Satellite-based coronagraphs, such as the one employed by SOHO, can create an “artificial eclipse” of the Sun to study the corona, but also face the challenge of scattered light via a phenomenon known as Fresnel-diffraction. Pasachoff and team hope to combine their observations with those being routinely carried out by NASA, the European Space Agency and the Royal Observatory in Belgium to characterize the solar corona and improve our understanding of the space weather environment. Pasachoff’s expedition is being assisted via support from the South African Astronomical Observatory, Nommo Astronomia, the Gabon Astronomy Society and the Gabon Space Agency. Veteran eclipse chaser and historian Michael Zeiler (@EclipseMaps) has also joined up with Pasachoff’s group in Gabon.

In space, the NASA/JAXA joint solar observing Hinode spacecraft and ESA’s Sun watching Proba-2 will also catch several partial eclipses from their respective perches in low Earth orbit. Expect to see these pics in the days following Sunday’s eclipse.

We’ll be dropping in more broadcasts as they come to our attention this weekend here at Universe Today. Planning an ad-hoc webcast of the eclipse? Let us know in the comments below! Even if it’s just a brief view of the rising partially eclipsed Sun from the beach, its worth the effort. Just remember that you’ll need a fairly long focal length (in the range of 200mm or longer) and a proper solar filter for the Sun to appear like anything more than a washed out dot in the broadcast. And always run a test of your rig beforehand!

Good luck, happy eclipse chasing, and don’t forget to send those eclipse pics to Universe Today!

 

Posted on by David Dickinson

Rare ‘Hybrid’ Solar Eclipse on November 3, 2013: How to See It

A partially eclipsed setting Sun as seen from Dallas, Texas on May 20th, 2012. This weekend's eclipse will offer U.S. East Coast residents a similar sunrise view. (Credit: Jason Major/Lights in the Dark).

It’s almost upon us. The final eclipse of 2013 occurs this coming weekend on Sunday, November 3rd. This will be the fifth eclipse overall, and the second solar eclipse of 2013. This will also be the only eclipse this year that features a glimpse of totality.

This eclipse is of the rare hybrid variety— that is, it will be an annular eclipse along the very first 15 seconds of its track before transitioning to a total as the Moon’s shadow sweeps just close enough to the Earth to cover the disk of the Sun along the remainder of its track.

An animation of the path of the November 3rd hybrid solar eclipse. (Credit: NASA/Goddard Space Flight Center).
An animation of the path of the November 3rd hybrid solar eclipse. (Credit: NASA/Goddard Space Flight Center).

How rare are hybrid solar eclipse? Of the 11,898 solar eclipses listed over a 5,000 year span from 1999 BC to 3000 AD in Fred Espenak’s Five Millennium Catalog of Solar Eclipses, only 569, or 4.8% are hybrids.

Who can see this eclipse?

People from northern South America, across the U.S. Eastern Seaboard and up through the Canadian Maritimes will see a brief partial solar eclipse finishing up around 30 minutes after local sunrise. The brief annular “ring of fire” portion of the eclipse begins at sunrise just ~1,000 kilometres east of Jacksonville, Florida, as it races eastward across the Atlantic. See our timeline, below.

Eclipse prospects for the US East Coast. (Courtesy of Michael Zeiler @EclipseMaps)
Eclipse prospects for the US East Coast. (Courtesy of Michael Zeiler @EclipseMaps)

Nearly all of Africa and the southern Mediterranean region including Spain will see partial phases of the eclipse, while greatest totality occurs just off of the coast of Liberia and heads for first landfall on the African continent over Wonga Wongue Reserve in Gabon. At this point, the duration of totality will already have shrunk back down to 1 minute and 7 seconds. The shadow of the Moon will then cross central Africa, headed for a short but brilliant sunset total eclipse over Uganda, Ethiopia, Kenya and Somalia.

The global path of this weekends eclipse-click to enlarge. (Credit: Michael Zeiler, @EclipseMaps).
The global path of this weekends eclipse-click to enlarge. (Credit: Michael Zeiler, @EclipseMaps).

This particular eclipse part of saros series 143 and is member 23 of the 72 eclipses in the cycle. The first eclipse in this saros occurred on March 7th, 1617, and the last one will occur on April 23rd, 2897.

Saros 143 also has a checkered place in  eclipse history. The last eclipse in this series crossed south eastern Asia on October 24th, 1995.

The first detailed picture of a solar eclipse was also taken of a saros 143 member on July 28, 1851. And one saros later, a total solar eclipse on August 7th, 1869 may have saved the butt of astronomer and explorer George Davidson while traversing the wilds of Alaska. And one more saros period later,  Dmitri Mendeleev (he of the modern periodic table) observed the total solar eclipse of August 19th, 1887 from a balloon.

A daguerreotype image of the 1851 eclipse captured by Berkowski of the Royal Observatory in Königsberg, Prussia. (Public domain image).
A daguerreotype image of the 1851 eclipse captured by Berkowski of the Royal Observatory in Königsberg, Prussia. (Public domain image).

We’ve compiled a brief worldwide timeline for the November 3rd hybrid eclipse. Keep in mind, the shift back off of Daylight Saving Time occurs on the same morning as the eclipse for North America, putting the U.S. East Coast  once again back to -5 hours off of Universal Time (UT):

10:04 UT: The partial phases of the eclipse begin.

11:05:17 UT: annular phases of the eclipse begin.

11:05:36 UT: The eclipse transitions from an annular to a total along its track.

12:46: The point of greatest eclipse, occurring off of the SW coast of Liberia along the coast of Africa. The path will be 57 kilometres wide at this point with a maximum duration for totality at 1 minute & 40 seconds.

14:27 UT: The total phases of the eclipse end.

15:28 UT: Partial phases end.

Remember that solar safety is paramount while observing an eclipse during all partial phases. This is especially critical, as millions of viewers along the U.S. East Coast are poised to catch the eclipse at sunrise over the Atlantic on Sunday. Use only glasses designed specifically for eclipse viewing or welder’s glass #14. One project headed by Astronomers Without Borders is also working to provide eclipse glasses to schools in Africa.

Students in Tanzania demonstrating proper eclipse viewing safety. (Credit: Astronomers Without Borders).
Students in Tanzania demonstrating proper eclipse viewing safety. (Credit: Astronomers Without Borders).

Projecting the Sun onto a wall or a piece of paper is also a safe method to observe the eclipse. Construction of a Sun Gun, a pinhole projector, or even using a spaghetti strainer or colander to project the partially eclipsed sun are all fun projects to try.

Shooting pictures of the rising eclipse is also possible using a DSLR. To capture the disk of the Sun plus an outline of the foreground, you’ll want to use a combination of low ISO 100 and a fast shutter speed (1/4000 or faster) and a zoom lens of at least 200mm or greater. Keep in mind, DO NOT look at the Sun through the camera’s view finder— simply set the focus to infinity and aim via projection. It’s worth practicing your technique a morning or two prior to the main event!

As the partial phase of the eclipse progresses, keep an eye out for “tiny crescents” that may litter the ground. These are caused by gaps in things such as leaves, latticework, etc that may act as natural “pinhole projectors”. Those lucky enough to stand in the path of totality may snare a look at shadow bands sweeping across the landscape as totality approaches, as well as catch a brief glimpse of Baily’s Beads and the pearly white corona of the Sun.

Totality will last less than a minute across most of central Africa, giving viewers a very hurried view before partial phases commence once more. Venus will be easily visible at magnitude -4.4 just 47 degrees east of the Sun. Unfortunately, prospects aren’t great for air or seaborne viewers in the mid-Atlantic to catch sight of comet ISON during the frenzied moments of totality, which will sit 50 degrees from the Sun between magnitude +7 & +8.

The sky over Gabon during mid-eclipse. (Created by the author using Starry Nite).
The sky over Gabon during mid-eclipse. (Created by the author using Starry Nite).

Weather prospects are an all-important consideration when planning for an eclipse. Jay Anderson maintains an outstanding site with projections tailor-made for each eclipse. For the U.S. East Coast, clear skies right down to the crucial eastern horizon will be key!

A recent surge in piracy off of the West Coast of Africa may also factor into travel considerations for eclipse chasers. You can actually monitor such activities on the high seas now in near real time. Perhaps one could take a page from Mark Twain’s A Connecticut Yankee in King Arthur’s Court, and impress any would-be-brigands with the glory of an impending solar eclipse…

Unfortunately, the International Space Station will have an orbit nearly perpendicular to the Earth-Moon-Sun syzygy, and won’t lend itself to any great prospects of a transit during the partial phases of the eclipse. ESA’s Proba-2 and JAXA’s Hinode will, however, see several partial eclipses from orbit:

Sunspot activity has also been on the upswing as of late, making for a photogenic Sun heading into the partial phases of the eclipse. A well-placed, naked eye Coronal Mass Ejection on the solar limb also isn’t out of the question. Eclipse historian and expert Michael Zeiler notes that a CME last occurred during a total solar eclipse way back in 1860.

Sunspot activity as of October 28th... will it stay active until this weekend's eclipse? (Photo by author).
Sunspot activity as of October 28th… will it stay active until this weekend’s eclipse? (Photo by author).

Totality for this eclipse passes over some wild and largely wifi free areas; few plans to broadcast the eclipse live have surfaced thus far.

Slooh plans a broadcast, as did a proposed Indiegogo project whose current status is unclear. BRCK also plans to broadcast the eclipse live from the shores of Lake Turkana, Kenya.  Got plans to webcast even the partial phases of the eclipse? Let us know!

And speaking of eclipse chasing, we plan on heading to the Florida Space Coast Sunday morning at o’dark thirty to nab the partial sunrise eclipse over the Atlantic.

And as always, the question posed immediately after totality is: when’s the next one? Well, the next annular eclipse graces Australia on April 29th, 2014. The U.S. will also see a partial solar eclipse on October 23rd next year… but totality will not touch the surface of our fair planet until a high Arctic eclipse on March 20th, 2015.

Good luck, clear skies, and safe journeys to all who are chasing after this one near and far, and don’t forget to post those pics to Universe Today’s Flickr page!

-See more of Michael Zeiler’s work at Eclipse Maps.

-Simulations were created using Starry Night Education Software.

Posted on by Nancy Atkinson

Why Is Comet ISON Green?

Recent images of Comet ISON along with spectral data. Credit and copyright: Chris Schur.

Undoubtedly, you’ve been seeing the recent images of Comet ISON now that it is approaching its close encounter with the Sun on November 28. ISON is currently visible to space telescopes like the Hubble and amateur astronomers with larger telescopes. But you might be wondering why many images show the comet with a green-ish “teal” or blue-green color.

Amateur Astronomer Chris Schur has put together this great graphic which provides information on the spectra of what elements are present in the comet’s coma.

For the conspiracy theorists out there, the green color is actually a good omen, and lots of comets display this color. The green color is a sign the comet is getting more active as gets closer to the Sun – meaning it is now putting on a good show for astronomers, and if it can continue to hold itself together, it might become one of the brightest comets in the past several years.

“ISON’s green color comes from the gases surrounding its icy nucleus,” says SpaceWeather.com’s Tony Phillips. “Jets spewing from the comet’s core probably contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C2). Both substances glow green when illuminated by sunlight in the near-vacuum of space.”

Comet ISON on October 4, 2013 as seen over Arizona, viewed with a 12.5" telescope, over an hour exposure time. Credit and copyright: Chris Schur.
Comet ISON on October 4, 2013 as seen over Arizona, viewed with a 12.5″ telescope, over an hour exposure time. Credit and copyright: Chris Schur.

Both are normally colorless gases that fluoresce a green color when excited by energetic ultraviolet light in sunlight.

And if those poisonous gasses sound dangerous, don’t worry. They are spread out in space much too thinly to touch us here on Earth. So don’t fall prey to fear mongers who are out to bilk the masses – like people did in 1910 when Comet Halley made a return to the skies and swindlers pitched their ‘gas masks’ and special ‘comet pills’ for protection. And of course, nothing happened.

But back to the color. Chris Schur provided this info along with his graphic:

Your readers may appreciate knowing why comets can appear this color. The background image is the shot I took with my 12.5″ and an ST10xme CCD camera for 20 minutes in mid-October. A pale coloration of the front of the coma is seen. To the lower left is a shot with the same instrument but with a 100 lpmm (line pair per millimeter) diffraction grating in front of the CCD chip to break out the spectra of the objects in the entire field.

Here ISON is faintly seen to the left of center, and the first order spectra a band to its right. But the real answer comes when we use the software called Rspec to analyze this band of light. The result is on the lower right. Normally reflected sunlight is rather flat and bland, and mostly that is what ISON is right now, reflected from dust. But labeled are two humps in the blue and green parts of the spectrum labeled “C2” for a carbon molecule. This blue/green emission pair is what gives ISON the color.

Chris notes that as the comet nears the Sun, astronomers and astrophotographers will be able to resolve more spectral details in the comet. “It will be exciting to watch the changes as more molecules pop out,” Chris said via email, “and possibly when it is closest to the Sun, we just may see some metal lines like iron or magnesium from MELTED vaporized rock. How exciting!”

And for those who insist there is something nefarious about Comet ISON, take a look at this FAQ from our friend Stuart Atkinson, who hosts the great site Waiting for ISON. He addresses the many conspiracy theories that are out there regarding this comet.

ISON FAQ Sept 9 jpg

Posted on by David Dickinson

Comet LINEAR Suddenly Brightens with Outburst: How to See It

Comet C/2012 X1 LINEAR as imaged by Howes, Guido & Nicolini on Monday, October 21st. (Credit: remanzacco.blogspot)

It’s swiftly becoming an “all comets, all the time” sort of observing season. The cyber-ink was barely dry on our “How to Spot Comet 2P/Encke” post this past Monday when we were alerted to another comet that is currently in the midst of a bright outburst.

That comet is C/2012 X1 LINEAR. Discovered on December 8th, 2012 by the ongoing Lincoln Near Earth Asteroid Research (LINEAR) survey based in Socorro, New Mexico, Comet X1 LINEAR was expected to peak out at about +12th magnitude in early 2014.

That all changed early this week, when amateur observers began to report a swift change in brightness for the otherwise nondescript comet. Japanese observer Hidetaka Sato reported the comet at magnitude +8.5 on October 20th, a full 5.5 magnitudes above its expected brightness of +14. Remember, the magnitude scale is logarithmic, and the lower the number, the brighter the object. Also, 5 magnitudes represent an increase in brightness of 100-fold.

Astronomers Nick Howes, Martino Nicolini and Ernesto Guido used the remote 0.5 metre iTelescope based in New Mexico on the morning of Monday, October 21st to confirm the outburst. Other amateurs and professional instruments are just now getting a look at the “new and improved” Comet X1 LINEAR low in the dawn sky. Romanian amateur observer Maximilian Teodorescu noted on yesterday’s Spaceweather that the comet was not visible through his 4.5 inch refractor, though it was easy enough to image.

Comet X1 LINEAR currently sits in the constellation Coma Berenices about mid-way between the stars Diadem, (Alpha Coma Berenices) and Beta Coma Berenices. Shining at +8.5 magnitude, the coma is about 85” across with a 10” bright central region. This gives X1 LINEAR the appearance of an unresolved +8th magnitude globular cluster. In fact, a classic globular and a star party fave known as M3 lies about 8 degrees away at the junction of the constellations Canes Venatici, Boötes and Coma Berenices. M3 shines at +7th magnitude and will make a great contrast on the hunt for the comet.

Unfortunately, the window of time to search for the comet is currently short. From latitude 30 degrees north, the comet sits only 15 degrees about the northeast horizon 30 minutes before local sunrise. The situation is a bit better for observers farther to the north, and mid-November sees the comet 20 degrees above the horizon in the dawn sky.

Comet X1 LINEAR is currently covering 40’ (2/3rds of a degree, or 1 1/3 the size of a Full Moon) a day, and will spend most of the month of November in the constellation Boötes. Keep in mind, X1 LINEAR is currently still on brightening trend “with a bullet.” Revised light curves now show it on track to reach magnitude +6 near perihelion early next year, but further brightening could still be in the cards for this one. Remember Comet 17P/Holmes a few years back? That one jumped from an uber-faint +17th magnitude to a naked eye brightness of +2.8 in less than 48 hours.

Comet X1 LINEAR will reach a perihelion of 1.6 Astronomical Units (A.U.s) from the Sun on February 21st, 2014, and pass 1.6 A.U.s from the Earth around June 28th, 2014. The comet has a high inclination of 44.4° degrees relative to the ecliptic, and is on a respectable 1872 year orbit.

Here are some notable dates for the comet through the end of 2013;

The path of Comet C/2012 X1 LINEAR from October 23 to November 28th. Click to enlarge. (Credit: Created using Starry Night Education Software).
The path of Comet C/2012 X1 LINEAR from October 23 to November 28th. Click to enlarge. (Credit: Created using Starry Night Education Software).

-November 2nd: Crosses into the constellation Boötes.

-November 6th: Passes near the +4.9th magnitude star 6 Boötis.

-November 16th: Passes near the bright star Arcturus.

-December 6th: Crosses into the constellation Serpens Caput.

-December 10th: Passes near the +5 magnitude star Tau1 Serpentis.

-December 14th: Comet X1 LINEAR sits only 8 degrees from Comet ISON.

-December 26th: Crosses into the constellation Hercules.

Note: “Passes near” on the above list denotes a pass closer than one degree, except as noted.

Now, we REALLY need the Moon to pass Last Quarter phase this coming Saturday so we can get a good look at all of these dawn comets! As of writing this, the current scorecard of binocular comets— comets with a brightness between magnitude +6 and +10 —sits at:

-2P Encke: +7.9 magnitude in Leo.

-C/2013 R1 Lovejoy: +8.7th magnitude in Canis Minor.

-C/2013 X1 LINEAR: +8.5th magnitude in Coma Berenices.

-C/2012 S1 ISON: +9.7th magnitude in Leo.

-C/2012 V2 LINEAR: +8.9th magnitude in Centaurus.

Comet X1 LINEAR on the morning of October 25th, as seen from latitude 30 degrees north 45 minutes prior to sunrise. (Created using Stellarium).
Comet X1 LINEAR on the morning of October 25th, as seen from latitude 30 degrees north 45 minutes prior to sunrise. (Created using Stellarium).

It’s also amusing to note how the method of notification for these sorts of outbursts has changed in recent years. I first heard of the outburst of X1 LINEAR on Monday evening via Twitter. Contrast this with Comet Holmes in 2007, which came to our attention via message board RSS feed. And way back in 1983, we all read about of the close passage of Comet IRAS-Araki-Alcock… weeks after it occurred!

Another curious phenomenon may also work its way through the news cycle. When Comet Holmes became a hit back in 2007, spurious reports of comets brightening became fashionable. If you were to believe everything you read on the web, it suddenly seemed like every comet was undergoing an outburst! This sort of psychological trend towards wish fulfillment may come to pass again as interest in comet outbursts mounts.

It’s also worth noting that, contrary to rumors flying around ye’ ole web, Comet X1 LINEAR is not following Comet ISON. The two are on vastly different orbits, and only roughly lie along the same line of sight as seen from our Earthly vantage point.

The orbital path of Comet X1 LINEAR. (Credit: The JPL Solar System Dynamics Small-Body Database Browser).
The orbital path of Comet C/2012 X1 LINEAR. (Credit: The JPL Solar System Dynamics Small-Body Database Browser).

And that’s it for our weekly (daily?) segment of “As the Comets Turn…” don’t forget to “fall back” one hour and plan your morning comet-hunting vigil accordingly this coming Sunday if you live in Europe-UK. North America still has until November 3rd to follow suit.

Happy comet hunting!

-Got a recent pic of Comet X1 LINEAR? be sure to post it in the Universe Today Flickr forum!

Posted on by David Dickinson

How to See This Season’s “Other” Comet: 2P/Encke

Comet 2P/Encke as imaged by Damian Peach on October 12th. (Credit: D. Peach)

2013 may well go down as “The Year of the Comet.” After over a decade punctuated by only sporadic bright comets such as 17P/Holmes, C/2011 W3 Lovejoy and C/2006 P1 McNaught, we’ve already had two naked eye comets visible this year by way of C/2012 F6 Lemmon and C/2011 L4 PanSTARRS. And of course, all eyes are on Comet C/2012 S1 ISON as it plunges towards perihelion on U.S. Thanksgiving Day, November 28th.

But there’s an “old faithful” of comets that’s currently in our solar neighborhood, and worth checking out as well. Comet 2P/Encke (pronounced EN-key) currently shines at magnitude +7.9 and is crossing from the constellation Leo Minor into Leo this week. In fact, Encke is currently 2 magnitudes— over 6 times brighter than Comet ISON —and is currently the brightest comet in our skies. Encke is expected to top out at magnitude +7 right around perihelion towards the end of November. Encke will be a fine binocular object over the next month, and once the Moon passes Last Quarter phase on October 26th we’ll once again have a good three week window for pre-dawn comet hunting. Comet Encke made its closest pass of the Earth for this orbit on October 17th at 0.48 Astronomical Units (A.U.s) distant. This month sees its closest passage to the Earth since 2003, and the comet won’t pass closer until July 11th, 2030.

The orbital path of Comet 2P/Encke. (Credit: The NASA/JPL Solar System Dynamics Small-Body Database Browser).
The orbital path of Comet 2P/Encke. (Credit: The NASA/JPL Solar System Dynamics Small-Body Database Browser).

This will be Comet Encke’s 62nd observed perihelion passage since its discovery by Pierre Méchain in 1786. Encke has the shortest orbit of any known periodic comet, at just 3.3 years. About every 33 years we get a favorable close pass of the comet, as last occurred in 1997, and will next occur in 2030.

But this year’s apparition of Comet Encke is especially favorable for northern hemisphere observers. This is due to its relatively high orbital inclination angle of 11.8 degrees and its passage through the morning skies from north of both the ecliptic and the celestial equator. Encke is about half an A.U. ahead of us in our orbit this month, crossing roughly perpendicular to our line of sight.

Note that Encke is also running nearly parallel to Comet ISON from our vantage point as they both make the plunge through the constellation Virgo into next month. Mark your calendars: both ISON and Encke will fit into a telescopic wide field of view around November 24th in the early dawn. Photo-op!

Here are some key dates to help you in your morning quest for Comet Encke over the next month:

-October 22nd: Crosses into the constellation Leo.

-October 24th: Passes near the +5.3 magnitude star 92 Leonis.

-October 25th: Passes near the +4.5 magnitude star 93 Leonis.

-October 27th: Passes briefly into the constellation Coma Berenices.

-October 29th: Passes near the +11th magnitude galaxy M98, and crosses into the constellation Virgo.

-October 30th: Passes near the +10th magnitude galaxy pair of M84 & M86.

2P Encke from 20 Oct to 20 Nov (Created using Starry Night Education Software).
The celestial path of Comet 2P/Encke from October 20th to 20 November 20th. Note that ISON is very near Encke on the final date. Click on the image to enlarge. (Created using Starry Night Education Software).

-November 2nd: Passes between the two +5th magnitude stars of 31 and 32 Virginis.

-November 3rd: A hybrid solar eclipse occurs across the Atlantic and central Africa. It may just be possible to spot comet Encke with binoculars during the brief moments of totality.

-November 4th: Passes near the +3.4 magnitude star Auva (Delta Virginis).

-November 7th: Crosses from north to south over the celestial equator.

-November 11th:  Passes near the +5.7th star 80 Virginis.

-November 17th: The Moon reaches Full, and enters into the morning sky.

-November 18th: Passes 0.02 A.U. (just under 3 million kilometers, or 7.8 Earth-Moon distances) from the planet Mercury. A good chance for NASA’s Messenger spacecraft to perhaps snap a pic of the comet?

-November 19th: Passes 1.5 degrees from Mercury and crosses into the constellation Libra.

-November 20th: Crosses to the south of the ecliptic plane.

-November 21st: Reaches perihelion, at 0.33 AU from the Sun.

-November 24th: Comet Encke passes just 1.25 degrees from Comet ISON. Both will have a western elongation of 15 degrees from the Sun.

-November 26th: Passes near the +4.5 magnitude star Iota Librae and the +6th magnitude star 25 Librae.

-December 1st: Crosses into the constellation Scorpius.

-December 5th: Enters into view of SOHO’s LASCO C3 camera.

Note: “Passes near” on the above list indicates a passage of Comet Encke less than one angular degree (about twice the size of a Full Moon) from an interesting object, except where noted otherwise.

Binoculars are your best bet for catching sight of Comet 2P/Encke. For middle northern latitude observers, Comet Encke reaches an elevation above 20 degrees from the horizon about two hours before local sunrise. Keep in mind, Europe and the U.K. “fall back” an hour to Standard Time this coming weekend on October 27th, and most of North America follows suit on November 3rd, pushing the morning comet vigil back an hour as well.

Two other comets are both currently brighter than ISON and also merit searching for: Comet C/2013 R1 Lovejoy, at +8.7th magnitude in Canis Minor, and Comet C/2012 X1 LINEAR, currently also in Coma Berenices and undergoing a minor outburst at magnitude +8.5.

Be sure to check these celestial wonders out as we prepare for the “Main Event” of Comet ISON in November 2013!

Posted on by David Dickinson

This Week’s Penumbral Lunar Eclipse and the Astronomy of Columbus

(Photo by Author)

You can always count on an eclipse to get you out of a delicate situation. Today is Columbus Day in the United States and Thanksgiving north of the border in Canada. Later this week also marks the start of the second eclipse season for 2013. Today, we thought we’d take a look at the circumstances for the first eclipse of the season kicking off this coming Friday night, October 18, as well as the fascinating role that eclipses played in the life and times of Christopher Columbus.

Friday’s event is a penumbral lunar eclipse, meaning that the Full Moon will only pass through the outer bright rim of the Earth’s shadow. Such events are subtle affairs, as opposed to total and partial lunar eclipses, which occur when the Moon enters the dark inner core, or umbra, of the Earth’s shadow. Still, you may just be able to notice a slight dusky shading on the lower southern limb of the Moon as it flirts with the umbra, barely missing it around the time of central eclipse at 23:51 Universal Time/ 7:51 PM Eastern Daylight Saving Time. Friday night’s penumbral is 3 hours and 59 minutes in duration, and 76.5% of the disk of the Moon will be immersed in the penumbra at maximum eclipse.

eclipse
The visibility footprint and circumstances of this week’s penumbral lunar eclipse. (Credit: Fred Espenak/NASA/GSFC).

Key Events occurring on Friday, October 18th:

21:50UT/5:50PM EDT: 1st contact with the Earth’s shadow.

23:51UT/7:51PM EDT: Mid-eclipse.

01:49UT(Oct 19th)/9:49PM EDT: Last contact. Eclipse ends.

The eclipse will be underway at moonrise for North and South America and occur at moonset for central Asia— Africa and Europe will see the entire eclipse. Standing on Earth’s Moon, an observer on the nearside would see a partial solar eclipse.

A simulation of Friday's lunar eclipse, looking back from Earth Moon at mid-eclipse. (Credit:
A simulation of Friday’s lunar eclipse, looking back from Moon at mid-eclipse. (Wikimedia Commons graphic in the Public Domain).

This eclipse is the 3rd and final lunar eclipse of 2013, and the 5th overall. It’s also the first in a series of four descending node eclipses, including the total lunar eclipse of October 8th next year.   It’s also the 52nd eclipse of 72 in the lunar saros series 117, which started on April 3rd, 1094 and will end with a final lunar eclipse on May 15th, 2356. Saros 117 produced its last total lunar eclipse in 1815 and its final partial in 1941.

Though penumbrals are slight events, we’ve been able to notice an appreciable difference before, during and after the eclipse photographically:

Penumbral I
Can you spy the difference? The May 18th, 2002 penumbral lunar eclipse before (left) and during mid-eclipse (right). Photos by Author.

Be sure to use identical exposure settings to catch this effect. Locations where the Moon rides high in the sky also stand the best chance of imaging the faint penumbral shading, as the Moon will be above the discoloring effects of the thicker air mass low to the horizon.

The Moon reaches descending node along the ecliptic about 20 hours after the end of the eclipse, and reaches apogee just over six days later on October 25th. The October Full Moon is also known as the Hunter’s Moon, providing a bit of extra illumination on the Fall hunt.

And this sets us up for the second eclipse of the season the next time the Moon crosses an ecliptic node, a hybrid (annular-total) solar eclipse spanning the Atlantic and Africa on November 3rd. More to come on that big ticket event soon!

In Columbus’s day, the Moon was often used to get a rough fix of a ship’s longitude at sea. Columbus was especially intrigued with the idea of using lunar eclipses to determine longitude. If you can note the position of the Moon in the sky from one location versus a known longitude during an event— such as first contact of the Moon with the Earth’s umbra during an eclipse —you can gauge your relative longitude east or west of the point. The sky moves 15 degrees, or one hour of right ascension overhead as we rotate under it. One of the earliest records of this method comes to us from Ptolemy, who deduced Alexander the Great’s position 30 degrees (2 hours) east of Carthage during the lunar eclipse of September 20th, 331 B.C. Alexander noted that the eclipse began two hours after sunset from his locale, while in Carthage it was recorded that the eclipse began at sunset.

A Jacob's crossstaff, a simple tool for measuring angles in the sky. (Photo by Author).
A Jacob’s cross staff, a simple tool for measuring angles in the sky. (Charles Towne Landing Historic Site Museum, Photo by Author).

Columbus was a student of Ptolemy, and used this method during voyages to and from the New World during the lunar eclipses of September 14th, 1494 and February 29, 1504. Of course, such a method is only approximate. The umbra of the Earth often appears ragged and indistinct on the edge of the lunar disk at the start of an eclipse, making it tough to judge the actual beginning of an eclipse by more than ten of minutes or so. And remember, you’re often watching from the pitching deck of a ship to boot!

Another problem also plagued Columbus’s navigation efforts: he favored a smaller Earth than we now know is reality. Had he listened to another Greek astronomer by the name of Eratosthenes, he would’ve gotten his measurements pretty darned close.

An eclipse also saved Columbus’s butt on one occasion. The story goes that tensions had come to a head between the locals and Columbus’s crew while stranded on the island of Jamaica in 1504. Noting that a lunar eclipse was about to occur on March 1st  (the evening of February 29th for North America), Columbus told the local leader that the Moon would rise “inflamed with wrath,” as indeed it did that night, right on schedule. Columbus then made a great show of pretending to pray for heavenly intersession, after which the Moon returned to its rightful color.  This kept a conniving Columbus and his crew stocked in supplies until a rescue ship arrived in June of that year.

A depiction of the 1504 lunar eclipse from the 1879 text Astronomie Populare by Camille Flammarion.
A depiction of the 1504 lunar eclipse from the 1879 text Astronomie Populare by Camille Flammarion.

Be sure to check out this Friday’s penumbral eclipse, and amaze your friends with the prediction of the next total lunar eclipse which occurs on U.S. Tax Day next year on April 15th, 2014. Can you do a better job of predicting your longitude than Columbus?

Posted on by David Dickinson

New Data: Will Comet ISON Survive its Close Perihelion Passage?

An analysis of the dust coma of comet ISON showing the evaporation of ice particles. (Credit: NASA/ESA J.-Y. Li (Planetary Science Institute and the Hubble ISON Imaging Science Team).

It’s the question on every astronomer’s mind this season, both backyard and professional: will Comet C/2012 S1 ISON survive perihelion?

Now, new studies released today at the American Astronomical Society’s 45th Annual Division for Planetary Sciences meeting being held this week in Denver suggests that ISON may have the “right stuff” to make it through its close perihelion passage near the Sun. This is good news, as Comet ISON is expected to be the most active and put on its best showing post-perihelion… if it survives.

Researchers Matthew Knight of the Lowell Observatory and Research Scientist Jian-Yang Li of the Planetary Science Institute both presented a compelling portrait of the characteristics and unique opportunities presented by the approach of comet ISON to the inner solar system.

Jian-Yang Li studied ISON earlier this year using Hubble before it passed behind the Sun from our Earthly vantage point. Li and researchers were able to infer the position and existence of a jet coming from the nucleus of the comet, which most likely marks the position of one of its rotational poles.

“We measured the rotational pole of the nucleus,” Li noted in a press release from the Planetary Science Institute. The pole indicates that only one side of the comet is being heating by the Sun on its way in until approximately one week before it reaches its closest point to the Sun.”

Could we be in for a “surge” of activity from ISON coming from around November 20th on?

Comet ISON as imaged from Aguadilla, (sp) Puerto Rico recently on october 6th. (Credit: Efrain Morales Rivera).
Comet ISON as imaged from Aguadilla, Puerto Rico recently on October 6th. (Credit: Efrain Morales Rivera).

Li also noted that the reddish color of the coma of ISON suggests an already active comet sublimating water ice grains as they move away from the nucleus. He also noted that time has been allocated to observe ISON using Hubble this week.

Next up, researcher Mathew Knight presented some encouraging news for ISON when it comes to surviving perihelion.

The findings were a result of numerical simulations carried out by Kevin Walsh and Knight, combined with a historical analysis of previous sun-grazing comets. Both suggest that comet nuclei smaller than 200 metres in diameter, with an average density or lower (for comets, that is) typically do not survive a close passage to the Sun.

Both researchers place the size of ISON’s nucleus in the range of 0.5 to 2 kilometres, comfortably above the 0.2 kilometre “shred limit” for its relative perihelion distance. ISON is not a technically Kreutz group sungrazer, though studies of the over 2,000 known Kreutz comets historically observed provide an interesting guideline for what might be in store for ISON. Four Kreutz comets, including C/2011 W3 Lovejoy and Comet C/1887 B1 partially survived perihelion to become “headless wonders,” while five, including Comet C/1965 S1 Ikeya-Seki — which ISON is often compared to — survived perihelion passage to become one of the great comets of the 20th century.

ISON will pass inside the Roche limit of the Sun, which is a distance of 2.4 million kilometres (for fluid bodies) and will be subject to temperatures approaching 5,000 degrees Fahrenheit on closest approach.

ISON is a first time visitor to the inner solar system. Discovered on September 21st, 2012 by Russian researchers Artyom Novichonok and Vitaly Nevsky participating in the International Scientific Optical Network, ISON will pass less than 1.2 million kilometres above the surface of the Sun on November 28th, 2013.

One interesting but little discussed factor highlighted in today’s press release was the retrograde versus prograde rotation of the cometary nucleus. A fast, prograde spin of an elongated nucleus may spell doom for ISON, as tidal forces will rip it apart. A retrograde rotator, however, is very likely to survive the encounter.

Thus far, there are no solid indications that ISON is indeed a retrograde rotator, although there are tantalizing hints that beg for further observations.

Li notes that it’s tough to infer a bias for comets like ISON to be retrograde over prograde rotators, as we’ve only got five historical comets to go by similar to ISON, and the breakdown is thus about 50/50 for and against.

ISON’s possible survival would validate both studies and their methods and give us more refined predictions for future comets.

“We’ve never discovered a sungrazer this far out,” Knight told Universe Today. “The rotation of ISON depends on the pole position (from Li’s study) and in theory, if we could get enough images, a proper morphology (for ISON) would emerge.”

Comet ISON imaged on October 5th from Long Beach, California. (Credit: Thad Szabo @AstroThad).
Comet ISON imaged on October 5th from Long Beach, California. (Credit: Thad Szabo @AstroThad).

The implications of this analysis is certainly good news for observers. If ISON survives perihelion, we would then have a brilliant dawn Christmas comet unfurling its tail off to the northeast in early December.

Of course, these findings are contrary to early cries of its demise, including the paper out of the Institute of Physics that has been circulating touting “The Impending Demise of ISON”. Read Universe Today editor Nancy Atkinson’s excellent synopsis on that, it’s a tale that just won’t seem to die.

And we’ve also done our skeptic’s duty of thoroughly debunking the mounting ISON lunacy, including its status as the harbinger for the “end of the world of the week,” as well as its inability to fulfill prophecy. But if we get a surge in ISON next month as researchers suggest, we fully expect the accompanying hype to crest as well.

The most recent observations put ISON at about +10th magnitude as it currently crosses the constellation Leo, near Mars and Regulus in the morning sky. We recently did an observing post tracking its plunge to perihelion in late November, and we’ve been diligently hunting for ISON with binoculars every morning pre-dawn.

We’re glad to have some positive science to report on for ISON. Things are looking up for a fine show come early December!

-Read the PSI press release on  JianYang Li’s findings as well as the original paper on ISON’s survival prospects by Matthew Knight.

Posted on by Bob King

Observing Alert: Rare Triple Transit Of Jupiter’s Moons Happens Friday Night (Oct. 11-12)

Jupiter with polka dot shadows cast by Io, Europa and Callisto as depicted around 1 a.m. EDT Oct. 12. Watch for the Great Red Spot to come into view during the transit. Created with Claude Duplessis' Meridian software

Talk about a great fall lineup. Three of Jupiter’s four brightest moons plan a rare show for telescopic observers on Friday night – Saturday morning Oct. 11-12. For a span of just over an hour, Io, Europa and Callisto will simultaneously cast shadows on the planet’s cloud tops, an event that hasn’t happened since March 28, 2004.

Who doesn’t remember their first time looking at Jupiter and his entourage of dancing moons in a telescope? Because each moves at a different rate depending on its distance from the planet, they’re constantly on the move like kids in a game of musical chairs. Every night offers a different arrangement.

Jupiter and its four brightest moons seen in a small telescope. Credit: Bob King
Jupiter and its four brightest moons seen in a small telescope. Credit: Bob King

Some nights all four of the brightest are strung out on one side of the planet, other nights only two or three are visible, the others hidden behind Jupiter’s “plus-sized” globe. Occasionally you’ll be lucky enough to catch the shadow of one of moons as it transits or crosses in front of the planet. We call the event a shadow transit, but to someone watching from Jupiter, the moon glides in front of the sun to create a total solar eclipse.

Since the sun is only 1/5 as large from Jupiter as seen from Earth, all four moons are large enough to completely cover the sun and cast inky shadows. To the eye they look like tiny black dots of varying sizes. Europa, the smallest, mimics a pinprick. The shadows of Io and Callisto are more substantial. Ganymede, the solar system’s largest moon at 3,269 miles (5,262 km), looks positively plump compared to the others. Even a small telescope magnifying around 50x will show it.

Jupiter on Sept. 24 with its moon Europa (at left) casting a pinhead black shadow on Jupiter's clouds. Credit: John Chumack
Jupiter on Sept. 24 with its moon Europa (at left) casting a pinhead black shadow on Jupiter’s clouds. Credit: John Chumack

The three inner satellites – Io, Europa and Ganymede – have shadow transits every orbit. Distant Callisto only transits when Jupiter’s tilt relative to Earth is very small, i.e. the plane of the planet’s moons is nearly edge-on from our perspective. Callisto transits occur in alternating “seasons” lasting about 3 years apiece. Three years of shadow play are followed by three years of shadowless misses. Single transits are fairly common; you can find tables of them online like this one from Project Pluto or plug in time and date into a free program like Meridian for a picture and list of times.

Because Io, Europa and Ganymede orbit in a 4:2:1 resonance (Io revolves four times around Jupiter in the time it takes Ganymede to orbit once; Europa completes two orbits for Ganymede's one) a "quadruple transit" is impossible. Credit: Matma Rex / Wikipedia
Because Io, Europa and Ganymede orbit in a 4:2:1 resonance (Io revolves four times around Jupiter in the time it takes Ganymede to orbit once; Europa completes two orbits for Ganymede’s one) it’s impossible for all three to line up – along with Callsto – for a “quadruple transit”. Credit: Matma Rex / Wikipedia

Seeing two shadows inch across Jupiter’s face is very uncommon, and three are as rare as a good hair day for Donald Trump. Averaged out, triple transits occur once or twice a decade. Friday night Oct. 11 each moon enters like actors in a play. Callisto appears first at 11:12 p.m. EDT followed by Europa and then Io. By 12:32 a.m. all three are in place.

Catch them while you can. Groups like these don’t last long. A little more than an hour later Callisto departs, leaving just two shadows.  You’ll find the details below. All times are Eastern Daylight or EDT. Subtract one hour for Central time and add four hours for BST (British Summer Time):

* Callisto’s shadow enters the disk – 11:12 p.m. Oct. 11
* Europa – 11:24 p.m.
* Io – 12:32 a.m.
** TRIPLE TRANSIT from 12:32 – 1:37 a.m.
* Callisto departs – 1:37 a.m.
* Europa departs – 2:01 a.m.
* Io departs – 2:44 a.m.

Looking at Jupiter from high above the plane of the solar system, we can picture better how shadow transits and eclipses happen. Credit: Garrett Serviss from "Pleasures of the Telescope" (annotations: Bob King)
Looking at Jupiter from high above the plane of the solar system in this diagram from more than a century ago, we can better picture how shadow transits and eclipses happen. The tiny disk of Io and the shadow of Ganymede are seen in transit; Callisto is about to be eclipsed by Jupiter’s shadow.  Credit: Garrett Serviss from “Pleasures of the Telescope” (annotations: Bob King)

The triple transit will be seen across the eastern half of the U.S., Europe and western Africa. Those living on the East Coast have the best view in the U.S. with Jupiter some 20-25 degrees high in the northeastern sky around 1 a.m. local time. Things get dicier in the Midwest where Jupiter climbs to only 5-10 degrees. From the mountain states the planet won’t  rise until Callisto’s shadow has left the disk, leaving a two-shadow consolation prize. If you live in the Pacific time zone and points farther west, you’ll unfortunately miss the event altogether.

From the Eastern Time Zone Jupiter will be well-placed in the eastern sky around the time of mid-transit. Created with Stellarium
From the Eastern Time Zone Jupiter will be well-placed in the eastern sky during the transit. Created with Stellarium

Key to seeing all three shadows clearly, especially if Jupiter is low in the sky, is steady air or what skywatchers call “good seeing”. The sky can be so clear you’d swear there’s a million stars up there, but a look through the telescope will sometimes show dancing, blurry images due to invisible air turbulence. That’s “bad seeing”. Unfortunately, bad seeing is more common near the horizon where we peer through a greater thickness of atmosphere. But don’t let that keep you inside Friday night. With a spell of steady air, all you need is a 4-inch or larger telescope magnifying around 100x to spot all three.

The March 28, 2004 triple transit. Shadows from left: Ganymede, Io and Callisto. You can also see the disks of Io (white dot) and Ganymede (blue dot) in this photo taken in infrared light by the Hubble Space Telescope. Credit: NASA/ESA
The March 28, 2004 triple transit. Shadows from left: Ganymede, Io and Callisto. You can also see the disks of Io (white dot) and Ganymede (blue dot) in this photo taken in infrared light by the Hubble Space Telescope. Credit: NASA/ESA

If bad weather blocks the view, there are two more triple transits coming up soon – a 95-minute-long event on June 3, 2014 starring Europa, Ganymede and Callisto (not visible in the Americas) and a 25-minute show on Jan. 24, 2015 featuring Io, Europa and Callisto and visible across Western Europe and the Americas. That’s it until dual triple transits in 2032.

 

Posted on by David Dickinson

A Fine Pair of Lunar Occultations for North America This Weekend

Pi Sagittarii moments before it was occulted by the Moon on August 10th, 2011. (Photo by Author).

Heads up, North American residents: our Moon is about to blot out two naked eye stars on Friday and Saturday night.

Such an event is known as an occultation, an astronomical term that has its hoary roots in astronomy’s pseudoscience ancestor of astrology. An occultation is simply when one astronomical body passes in front of another from our line of sight. There’s nothing quite like watching a star disappear on the dark limb of the Moon. In a universe where events often transpire over periods of time longer than a human life span, occultations are abrupt affairs to witness.

Close double stars have also been teased out of occultation data, winking out in a quick, step-wise fashion. If an occultation such as the two this weekend occurs while the Moon is waxing towards Full, we get the added advantage of watching the action on the leading dark limb of the Moon during convenient early evening hours.

Beta Capricorni on the dark limb of the Moon Saturday night. (Created by the author using Starry Night).
Beta Capricorni on the dark limb of the Moon Saturday night. (Created by the author using Starry Night).

First up is the occultation of the +3.9th magnitude star Rho Sagittarii on Friday night, October 11th. Central conjunction for this occultation occurs at 00:40 Universal Time (UT) early on the morning of the 12th. The Moon will be at a 51% illuminated waxing gibbous phase, having passed First Quarter just prior to the start of the occultation at 7:02 PM EDT/23:02 UT on the 11th. The sunset terminator line at the start of the occultation will bisect the central U.S., and observers east of the Mississippi will get to witness the entire event. The southern graze line will cross Cuba and Guatemala. Note that the Moon will also pass its most southern declination for this lunation just two days prior on October 9th at 23:00 UT/7:00 PM EDT, at a declination of -19.6 degrees.  This is one of the Moon’s most southern journeys for 2013, meaning that it will still ride fairly far to the south in the sky during this weekend’s occultations.

The occultation of Rho Saggitarii by the Moon for the night of October 11th. (rendered using Occult 4.1.02 software).
The occultation of Rho Sagittarii by the Moon for the night of October 11th. the dashed line indicates where the occultation will occur in the daytime; east of this region, the occultation occurs after sunset. (rendered using Occult 4.1.02 software).

Rho Sagittarii is an F-type star 122 light years distant. Stick around until February 23rd, 2046, and you’ll get to see an even rarer treat, when the planet Venus occults the very same star. Just south of the Rho Sagittarii pair lies the region from which the Wow! Signal was detected in 1977.

The Moon moves at an average speed of just over a kilometre a second in its orbit about the Earth, and traverses roughly the apparent distance of its angular size of 30’ in one hour. The duration of occultations as seen from their center line take about an hour from ingress to egress, though its much tougher to watch a star reappear on the bright limb of the Moon!

And the night of Saturday, October 12th finds the 62% illuminated waxing gibbous Moon occulting an even brighter star across roughly the same region. The star is +3.1 magnitude Beta Capricorni, which also goes by the Arabic name of Dabih, meaning “the butcher.”  Dabih is also an interesting double star with a +6th magnitude component 3.5’ away from the +3rd magnitude primary. Dabih is an easy split with binoculars, and it will be fun to watch the two components pass behind the Moon Saturday night. This occultation also occurs the night of October 12th which is traditionally Fall Astronomy Day. If you’re hosting a star party this coming Saturday night, be sure to catch the well-timed occultation of Beta Capricorni! The central conjunction for this event occurs at 01:27 UT on the morning of the 13th, and North American observers east of the Rockies will get to see the entire event.

(Rendered using Occult 4.1.0.2 software).
The occultation footprint of Beta Capricorni for the night of October 12th. (Rendered using Occult 4.1.0.2 software).

Beta Capricorni is 328 light years distant, putting the physical separation of the B component at about a third of a light year away from the primary star at 21,000 astronomical units distant. “Beta B” thus takes about 700,000 years to orbit its primary! It’s also amazing to think that those fusion-born photons took over three centuries to get here, only to be rudely “interrupted” by the bulk of our Moon in the very last second of their journey.

And be sure to keep an eye on the primary star as it winks out, as it’s a known spectroscopic triple star with unseen companions in respective 9 and 1374 day orbits. Dabih may just appear to “hang” on the jagged lunar limb as those close companions wink out in a step-wise fashion.

Both occultations are bright enough to watch with the naked eye, although a standard set of 10x 50 binoculars will provide a fine view. The ingress of an occultation is also an excellent event to catch on video, and if you’ve got WWV radio running audio in the background, you can catch the precise time that the star disappears from your locale.

Note: WWV radio is still indeed broadcasting through the ongoing U.S. government shutdown, though they’re operated by NOAA & the NIST.

The International Occultation and Timing Association is always interested in reports of occultations carried out by amateur astronomers. Not only can this reveal or refine knowledge of close double stars, but a series of occultation observations from precisely known locations can map the profile of the lunar limb.

Be sure to catch both events this U.S. Columbus Day/Canadian Thanksgiving Day weekend, and send those pics in to Universe Today!

Precise timings for the ingress and egress of each lunar occultations for major North American cities can be found at the following pages:

– Rho Sagittarii

– Beta Capricorni